java.lang.Objectjava.util.ResourceBundle
public abstract class ResourceBundle
Resource bundles contain locale-specific objects. When your program needs a locale-specific resource, a String for example, your program can load it from the resource bundle that is appropriate for the current user's locale. In this way, you can write program code that is largely independent of the user's locale isolating most, if not all, of the locale-specific information in resource bundles.
This allows you to write programs that can:
Resource bundles belong to families whose members share a common base name, but whose names also have additional components that identify their locales. For example, the base name of a family of resource bundles might be "MyResources". The family should have a default resource bundle which simply has the same name as its family - "MyResources" - and will be used as the bundle of last resort if a specific locale is not supported. The family can then provide as many locale-specific members as needed, for example a German one named "MyResources_de".
Each resource bundle in a family contains the same items, but the items have been translated for the locale represented by that resource bundle. For example, both "MyResources" and "MyResources_de" may have a String that's used on a button for canceling operations. In "MyResources" the String may contain "Cancel" and in "MyResources_de" it may contain "Abbrechen".
If there are different resources for different countries, you can make specializations: for example, "MyResources_de_CH" contains objects for the German language (de) in Switzerland (CH). If you want to only modify some of the resources in the specialization, you can do so.
When your program needs a locale-specific object, it loads the ResourceBundle class using the getBundle method:
ResourceBundle myResources = ResourceBundle.getBundle("MyResources", currentLocale);
Resource bundles contain key/value pairs. The keys uniquely identify a locale-specific object in the bundle. Here's an example of a ListResourceBundle that contains two key/value pairs:
public class MyResources extends ListResourceBundle { protected Object[][] getContents() { return new Object[][] { // LOCALIZE THE SECOND STRING OF EACH ARRAY (e.g., "OK") {"OkKey", "OK"}, {"CancelKey", "Cancel"}, // END OF MATERIAL TO LOCALIZE }; } }
You retrieve an object from resource bundle using the appropriate getter method. Because "OkKey" and "CancelKey" are both strings, you would use getString to retrieve them:
button1 = new Button(myResources.getString("OkKey")); button2 = new Button(myResources.getString("CancelKey"));
Besides getString, ResourceBundle also provides a method for getting string arrays, getStringArray, as well as a generic getObject method for any other type of object. When using getObject, you'll have to cast the result to the appropriate type. For example:
int[] myIntegers = (int[]) myResources.getObject("intList");
The Java 2 platform provides two subclasses of ResourceBundle, ListResourceBundle and PropertyResourceBundle, that provide a fairly simple way to create resources. As you saw briefly in a previous example, ListResourceBundle manages its resource as a list of key/value pairs. PropertyResourceBundle uses a properties file to manage its resources.
If ListResourceBundle or PropertyResourceBundle do not suit your needs, you can write your own ResourceBundle subclass. Your subclasses must override two methods: handleGetObject and getKeys().
// default (English language, United States) public class MyResources extends ResourceBundle { public Object handleGetObject(String key) { if (key.equals("okKey")) return "Ok"; if (key.equals("cancelKey")) return "Cancel"; return null; } } // German language public class MyResources_de extends MyResources { public Object handleGetObject(String key) { // don't need okKey, since parent level handles it. if (key.equals("cancelKey")) return "Abbrechen"; return null; } }
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protectedResourceBundleparent
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publicResourceBundle()
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public finalStringgetString(Stringkey)
![]()
(String)![]()
getObject![]()
(key).
public finalString[]getStringArray(Stringkey)
![]()
(String[])![]()
getObject![]()
(key).
public finalObjectgetObject(Stringkey)
publicLocalegetLocale()
protected voidsetParent(ResourceBundleparent)
public static finalResourceBundlegetBundle(StringbaseName)
![]()
getBundle(baseName, Locale.getDefault(), this.getClass().getClassLoader()),
public static finalResourceBundlegetBundle(StringbaseName,ResourceBundle.Controlcontrol)
getBundle(baseName, Locale.getDefault(), this.getClass().getClassLoader(), control),
public static finalResourceBundlegetBundle(StringbaseName,Localelocale)
![]()
getBundle(baseName, locale, this.getClass().getClassLoader()),
public static finalResourceBundlegetBundle(StringbaseName,LocaletargetLocale,ResourceBundle.Controlcontrol)
getBundle(baseName, targetLocale, this.getClass().getClassLoader(), control),
public staticResourceBundlegetBundle(StringbaseName,Localelocale,ClassLoaderloader)
Conceptually, getBundle uses the following strategy for locating and instantiating resource bundles:
getBundle uses the base name, the specified locale, and the default locale (obtained from
Locale.getDefault
) to generate a sequence of
candidate bundle names
. If the specified locale's language, country, and variant are all empty strings, then the base name is the only candidate bundle name. Otherwise, the following sequence is generated from the attribute values of the specified locale (language1, country1, and variant1) and of the default locale (language2, country2, and variant2):
Candidate bundle names where the final component is an empty string are omitted. For example, if country1 is an empty string, the second candidate bundle name is omitted.
getBundle then iterates over the candidate bundle names to find the first one for which it can instantiate an actual resource bundle. For each candidate bundle name, it attempts to create a resource bundle:
If no result resource bundle has been found, a MissingResourceException is thrown.
getBundle iterates over the candidate bundle names that can be obtained by successively removing variant, country, and language (each time with the preceding "_") from the bundle name of the result resource bundle. As above, candidate bundle names where the final component is an empty string are omitted. With each of the candidate bundle names it attempts to instantiate a resource bundle, as described above. Whenever it succeeds, it calls the previously instantiated resource bundle's
Once a result resource bundle has been found, its parent chain is instantiated.
setParent
method with the new resource bundle, unless the previously instantiated resource bundle already has a non-null parent.
getBundle caches instantiated resource bundles and may return the same resource bundle instance multiple times.
The baseName argument should be a fully qualified class name. However, for compatibility with earlier versions, Sun's Java 2 runtime environments do not verify this, and so it is possible to access PropertyResourceBundles by specifying a path name (using "/") instead of a fully qualified class name (using ".").
Code assignments in ISO 639 have changed over time for a few languages. When the locale (either the specified one or the default) uses one of the languages where a new language code replaced an old one, the default implementation of getBundle instantiates resource bundles with candidate bundle names with both old and new language codes, using the locale's language code first. For example, the table below shows the candidate bundle names generated for three request locales involving Hebrew; the same pattern is used for Indonesian and Yiddish.
For Norwegian, ISO 639 added two new specialized language codes in addition to an older, more generic one. The table shows the candidate bundle names generated for the locales involving either of the language codes.
ResourceBundle myResources = ResourceBundle.getBundle("MyResources", currentLocale);
Resource bundles contain key/value pairs. The keys uniquely identify a locale-specific object in the bundle. Here's an example of a ListResourceBundle that contains two key/value pairs:
public class MyResources extends ListResourceBundle { protected Object[][] getContents() { return new Object[][] { // LOCALIZE THE SECOND STRING OF EACH ARRAY (e.g., "OK") {"OkKey", "OK"}, {"CancelKey", "Cancel"}, // END OF MATERIAL TO LOCALIZE }; } }
You retrieve an object from resource bundle using the appropriate getter method. Because "OkKey" and "CancelKey" are both strings, you would use getString to retrieve them:
button1 = new Button(myResources.getString("OkKey")); button2 = new Button(myResources.getString("CancelKey"));
Besides getString, ResourceBundle also provides a method for getting string arrays, getStringArray, as well as a generic getObject method for any other type of object. When using getObject, you'll have to cast the result to the appropriate type. For example:
int[] myIntegers = (int[]) myResources.getObject("intList");
The Java Platform provides two subclasses of ResourceBundle, ListResourceBundle and PropertyResourceBundle, that provide a fairly simple way to create resources. As you saw briefly in a previous example, ListResourceBundle manages its resource as a list of key/value pairs. PropertyResourceBundle uses a properties file to manage its resources.
If ListResourceBundle or PropertyResourceBundle do not suit your needs, you can write your own ResourceBundle subclass. Your subclasses must override two methods: handleGetObject and getKeys().
MyResources.class MyResources.properties MyResources_fr.properties MyResources_fr_CH.class MyResources_fr_CH.properties MyResources_en.properties MyResources_es_ES.classThe contents of all files are valid (that is, public non-abstract subclasses of ResourceBundle for the ".class" files, syntactically correct ".properties" files). The default locale is Locale("en", "GB").
Calling getBundle with the shown locale argument values instantiates resource bundles from the following sources:
The file MyResources_fr_CH.properties is never used because it is hidden by MyResources_fr_CH.class. Likewise, MyResources.properties is also hidden by MyResources.class.
// default (English language, United States) public class MyResources extends ResourceBundle { public Object handleGetObject(String key) { if (key.equals("okKey")) return "Ok"; if (key.equals("cancelKey")) return "Cancel"; return null; } public Enumeration<String> getKeys() { return Collections.enumeration(keySet()); } // Overrides handleKeySet() so that the getKeys() implementation // can rely on the keySet() value. protected Set<String> handleKeySet() { return new HashSet<String>(Arrays.asList("okKey", "cancelKey")); } } // German language public class MyResources_de extends MyResources { public Object handleGetObject(String key) { // don't need okKey, since parent level handles it. if (key.equals("cancelKey")) return "Abbrechen"; return null; } protected Set<String> handleKeySet() { return new HashSet<String>(Arrays.asList("cancelKey")); } }
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protected
ResourceBundle
parent
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public
ResourceBundle
()
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public final
String
getString
(
String
key)
(String)
getObject
(key).
public final
String
[]
getStringArray
(
String
key)
(String[])
getObject
(key).
public final
Object
getObject
(
String
key)
public
Locale
getLocale
()
protected void
setParent
(
ResourceBundle
parent)
public static final
ResourceBundle
getBundle
(
String
baseName)
getBundle(baseName, Locale.getDefault(), this.getClass().getClassLoader()),
public static final
ResourceBundle
getBundle
(
String
baseName,
ResourceBundle.Control
control)
getBundle(baseName, Locale.getDefault(), this.getClass().getClassLoader(), control),
public static final
ResourceBundle
getBundle
(
String
baseName,
Locale
locale)
getBundle(baseName, locale, this.getClass().getClassLoader()),
public static final
ResourceBundle
getBundle
(
String
baseName,
Locale
targetLocale,
ResourceBundle.Control
control)
getBundle(baseName, targetLocale, this.getClass().getClassLoader(), control),
public static
ResourceBundle
getBundle
(
String
baseName,
Locale
locale,
ClassLoader
loader)
getBundle uses the base name, the specified locale, and the default locale (obtained from
Locale.getDefault
Conceptually, getBundle uses the following strategy for locating and instantiating resource bundles:
) to generate a sequence of
candidate bundle names
. If the specified locale's language, country, and variant are all empty strings, then the base name is the only candidate bundle name. Otherwise, the following sequence is generated from the attribute values of the specified locale (language1, country1, and variant1) and of the default locale (language2, country2, and variant2):
Candidate bundle names where the final component is an empty string are omitted. For example, if country1 is an empty string, the second candidate bundle name is omitted.
getBundle then iterates over the candidate bundle names to find the first one for which it can instantiate an actual resource bundle. For each candidate bundle name, it attempts to create a resource bundle:
If no result resource bundle has been found, a MissingResourceException is thrown.
Once a result resource bundle has been found, its parent chain is instantiated.
getBundle iterates over the candidate bundle names that can be obtained by successively removing variant, country, and language (each time with the preceding "_") from the bundle name of the result resource bundle. As above, candidate bundle names where the final component is an empty string are omitted. With each of the candidate bundle names it attempts to instantiate a resource bundle, as described above. Whenever it succeeds, it calls the previously instantiated resource bundle's
setParent
method with the new resource bundle, unless the previously instantiated resource bundle already has a non-null parent.
getBundle caches instantiated resource bundles and may return the same resource bundle instance multiple times.
The baseName argument should be a fully qualified class name. However, for compatibility with earlier versions, Sun's Java SE Runtime Environments do not verify this, and so it is possible to access PropertyResourceBundles by specifying a path name (using "/") instead of a fully qualified class name (using ".").
Example:
The following class and property files are provided:
MyResources.class
MyResources.properties
MyResources_fr.properties
MyResources_fr_CH.class
MyResources_fr_CH.properties
MyResources_en.properties
MyResources_es_ES.class
The contents of all files are valid (that is, public non-abstract subclasses of ResourceBundle for the ".class" files, syntactically correct ".properties" files).
The default locale is Locale("en", "GB").
Calling getBundle with the shown locale argument values instantiates resource bundles from the following sources:
The file MyResources_fr_CH.properties is never used because it is hidden by MyResources_fr_CH.class.
public static ResourceBundle getBundle(String baseName, Locale targetLocale, ClassLoader loader, ResourceBundle.Control control)
Locale |
format |
Locale("de", "DE") |
java.class |
Locale("de", "DE") |
java.properties |
Locale("de") | java.class |
Locale("de") | java.properties |
Locale("") |
java.class |
Locale("") | java.properties |
During the resource bundle loading process above, this factory method looks up the cache before calling the control.newBundle method. If the time-to-live period of the resource bundle found in the cache has expired, the factory method calls the control.needsReload method to determine whether the resource bundle needs to be reloaded. If reloading is required, the factory method calls control.newBundle to reload the resource bundle. If control.newBundle returns null, the factory method puts a dummy resource bundle in the cache as a mark of nonexistent resource bundles in order to avoid lookup overhead for subsequent requests. Such dummy resource bundles are under the same expiration control as specified by control.
All resource bundles loaded are cached by default. Refer to control.getTimeToLive for details.
The following is an example of the bundle loading process with the default ResourceBundle.Control implementation.
Conditions:
First, getBundle tries loading a resource bundle in the following sequence.
At this point, getBundle finds foo/bar/Messages.properties, which is put on hold because it's the base bundle. getBundle calls control.getFallbackLocale("foo.bar.Messages", Locale.ITALY) which returns Locale.FRENCH. Next, getBundle tries loading a bundle in the following sequence.
getBundle finds foo/bar/Messages_fr.properties and creates a ResourceBundle instance. Then, getBundle sets up its parent chain from the list of the candiate locales. Only foo/bar/Messages.properties is found in the list and getBundle creates a ResourceBundle instance that becomes the parent of the instance for foo/bar/Messages_fr.properties.
public static final void clearCache()
public static final void clearCache(ClassLoader loader)
protected abstract Object handleGetObject(String key)
public abstract Enumeration<String> getKeys()
public boolean containsKey(String key)
public Set<String> keySet()
protected Set<String> handleKeySet()
The default implementation returns a Set of the keys returned by the getKeys method except for the ones for which the handleGetObject method returns null. Once the Set has been created, the value is kept in this ResourceBundle in order to avoid producing the same Set in the next calls. Override this method in subclass implementations for faster handling.